1. Field of the Invention
The present invention generally relates to a new and improved apparatus for plugging a pressure piping system and to a new and improved method of securing the plug and supporting structure within the piping system.
2. Description of the Prior Art
Hot tapping a piping system involves cutting a hole in a filled or pressurized pipe, tank, container or pressure vessel without loss of material inside or depressurization. Hot tapping may be known by other names such as pressure tapping, wet tapping, side cutting and the like depending on the industry or location, but regardless of what the method is called, this process allows new lines and systems to be tied into those that are existing and pressurized. It also permits under pressure instrument insertion, on-stream bypass installation, re-routing, and line plugging.
Hot tapping is normally accomplished by surrounding a portion of the pipe or vessel by a pressure tight flange or fitting containing a cutting tool and cutting the pipe or vessel wall by machining or abrasion action. Connections may then be made to the flange or fitting to provide temporary or permanent bypasses around or taps to the line or vessel. The cutting tool is then removed and the connection between the cutting tool and flange or vessel is plugged. If the tap or bypass is a temporary one, the connection between the tap or bypass is also plugged upon removal of the temporary tap or bypass. The hot tapping and subsequent line plugging described above is used, for example, when working on a system and installing control.
In plugging a line after a basic hot tap, a plug is inserted into the flange or fitting and held in position by a variety of supporting structures. These supporting structures are important in that they maintain the plug in position under substantial pressure. In addition, the supporting structures must also allow the plug to be easily installed and removed without damage to any of the structure, and minimize the possibility of failure under long term exposure to pressure within the piping system.
One prior art method of mounting a plug within a piping system employs a threaded bore extending through the flange of the piping system and a retaining device. The retaining device includes a threaded actuator extending through the threaded bore. The actuator has a T-shaped head that mounts in a T-shaped slot in a movable segment that engages a groove in the plug. An O-ring is positioned about the actuator to prevent leaks. The above-described prior art system requires a rather long, threaded hole or bore to be machined into the flange, and such a hole or bore is difficult to clean and to maintain.
Also, in such a prior art retaining device, the entire actuator must be rotated in order to bring the segment into engagement with the plug. Therefore, the ring around the actuator is also rotated, and is worn when such rotation occurs. The prior art device is also susceptible to possible damage to the O-ring during installation, which could result in eventual deterioration and failure of the O-ring. This prior art system also requires some means for retaining the segments in place when they are extended in the absence of a plug. This is generally accomplished by drilling holes through the flange and mounting bolts therein to limit the travel of the segment, a process which is time consuming and costly. In addition, such prior art systems only accommodate a specific size flange and plug thus, requiring complete new assemblies for variation in plug size and flange size.